Display technologies have substantially impacted basic and applied research applications ranging from drug discovery to materials synthesis (see, e.g., Clackson and Wells (1994) Trends In Biotech. 12(5):173-184; Lee et al. (2002) Science 296 (5569):892-859; and Nixon (2002) Curr. Pharm. Biotechnol. 3(1):1-12). The strength of these methods derives from the ability to generate libraries containing billions of diverse molecules using the biosynthetic machinery of the cell, and subsequently, to identify rare desired peptides and proteins using selection or high-throughput screening methods. For example, display systems have been routinely employed to isolate and engineer proteins including, for example, antibodies.
Surface display libraries, for example, of antibodies, allow for the enrichment of specific binding clones by subjecting the organism displaying the binding molecule (e.g., phage and yeast) to successive rounds of selection (e.g., Kretzschmar et al. 2002, Curr Opin Biotechol 13: 598-602). Display systems include mRNA and ribosome display, eukaryotic virus display, and bacterial and yeast cell surface display (see, e.g., Wilson et al. 2001 PNAS 98(7):3750-3511; Muller et al. (2003) Nat. Biotechnol. 3:312; Bupp and Roth (2002) Md. Ther. 5(3):329-3513; Georgiou et al. (1997) Nat. Biotechnol. 15(1):29-3414; and Boder and Wittrup (1997) Nature Biotech. 15(6):553-557). Surface display methods are attractive since they enable application of fluorescence-activated cell sorting (FACS) for library analysis and screening (see, e.g., Georgiou (2000) Adv. Protein Chem. 55:293-315; and Boder et al. (2000) PNAS 97(20):10701-10705). However, available surface display systems generally rely on the fusion of a protein of interest to a coat protein or cell wall protein which anchors the protein of interest on the cell surface. Such fusion may affect proliferation of the host and/or the expression level of the display protein. Use of naturally occurring coat proteins of higher eukaryotic species, such as yeast, may be better tolerated than phage coat proteins but the requirement of normal assembly into the cell wall of such native proteins can impose limitations on the host species that may be used for or support display.